Unable to Rebase in IE, Rebase in Chrome produces error, but refreshing shows success

Summary

As reported by customer

From a merge request, I am unable to initiate a rebase command via IE 11, which results in an error "Somthing went wrong". I then attempt the rebase in Chrome 60, which appears to initiate properly, but then indicates an error that the source branch HEAD recently changed and I should try refershing. However, on refreshing it appears to have rebased successfully.

Steps to reproduce

Attempt to rebase using IE11 (Reproduction steps are available in internal ticket: https://gitlab.zendesk.com/agent/tickets/82353

Relevant logs and/or screenshots

==> /var/log/gitlab/gitlab-rails/production.log <==
Started POST "/matthew_wiesen/openssl/merge_requests/1/rebase" for xxx.xx.xx.xx at xxxxxxxxxxxxx

ActionDispatch::ParamsParser::ParseError (822: unexpected token at 'undefined'):
lib/gitlab/middleware/readonly_geo.rb:30:in `call'
lib/gitlab/request_context.rb:18:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'

Possible fixes

Correctly parse response in IE11